Method and apparatus for depositing coplanar microelectronic interconnectors using a compliant mold

ABSTRACT

A method and apparatus for the formation of coplanar electrical interconnectors. Solder material is deposited onto a wafer, substrate, or other component of an electrical package using a complaint mold such that the terminal ends of the solder material being deposited, i.e., the ends opposite to those forming an attachment to the wafer, substrate, or other component of an electrical package are coplanar with one another. A complaint mold is used having one or more conduits for receiving solder material and having a compliant side and a planar side. The compliant side of the mold is positioned adjacent to the wafer, substrate, or other component of an electrical package allowing solder material to be deposited onto the surface thereof such that the planar side of the compliant mold provides coplanar interconnectors. An Injection Molded Solder (IMS) head can be used as the means for filling the conduits of the compliant mold of the present invention.

FIELD OF THE INVENTION

The present invention relates generally to the formation of coplanarinterconnectors, and more particularly relates to the field ofdepositing solder material interconnectors on wafers, substrates, andany other electronic packages requiring solder material microelectronicinterconnections.

BACKGROUND OF THE INVENTION

As used herein the term “interconnector” means a solder-material-depositattached to an electrical component capable of being electricallyinterconnected to another electrical component. In addition, the term“microelectronic interconnection” is meant to mean the connectionestablished between two electrical components by one or moreinterconnectors in a microelectronic package. Finally, the term “soldermaterial” should be understood to include traditional solders as knownto those skilled in the art, as well as less traditional materials likelead free solders, polymer based materials, and various othercombinations thereof.

Presently, there are a wide variety of microelectronic packageinterconnections used in modern semiconductor devices. Suchmicroelectronic package interconnections include connections between: ICchips (chip-on-chip stacking), IC chips and carriers, carriers andsubstrates, and substrates and printed circuit cards. As the need forgreater area array densities for microelectronic interconnectionsincreases, improved techniques are developing that allow for soldermaterial to be deposited onto receiving pads contained on wafers andsubstrates, e.g., bottom layer metallurgy (BLM) and bottom surfacemetallurgy (BSM).

Related to IC chip and chip carrier interconnections recent developmentshave been made in flip-chip solder bump technologies in response toincreased demand for electrical performance, functionality, andreliability offered by wafer bumping as compared to other technologicalsolutions like wire bonding for example. Using flip-chip technology,solder is deposited on the receiving pads of a wafer in the form ofsmall bumps through the process known as wafer bumping. Unlike wirebonding, wafer bumping allows for area array interconnections across theentire surface of the chip to be deposited with solder bumps that aresubsequently microelectronically interconnected to a substrate using asolder reflow process. At the substrate level, solder column connection(SCC) or ceramic column grid array (CCGA) or copper column grid array(CuCGA) technologies have developed providing a process for theattachment of solder columns to the metalicized pads of a substrate(e.g., BSM). Such techniques avoid the disadvantages associated with pingrid array (PGA) interconnections at this level such as higher cost andlower interconnection density.

For CCGA and CuCGA the PbSn (90%/10%), which has melting point greaterthan 260° C., or copper columns can be joined to a board using PbSneutectic solder (37%/63%), which has a melting point of 183° C., or leadfree solders, which have melting points between 217° C. and 231° C.These structures permit a solder column or copper column to be joinedwhile maintaining a lower joining temperature, for connection to theboard, with use of eutectic PbSn solder or lead free solders such asSnAgCu, SnAg, or SnCu. This type of structure also permits a largerheight between package and board to be maintained for the solder columnand joining solder metallurgy by creating a non-melting solder columnand solder melting joining composition for surface attachment to theboard. In this multi-solder structure, and for copper column plus solderattachment structures, the resulting product benefits from a longer lifeprior to fatigue failures of the mounting to a board in reliabilitytesting and in product application for these surface mount attachstructures as compared to lower height ball grid array mounting to aboard, for similar package sizes.

As the types of interconnectors increases efficient ways for theirformation and placement are also being developed. Injection-moldedsolder (hereinafter “IMS”) technology has been steadily developing inthe field of microelectronic interconnections. A discussion of waferbumping using IMS head technologies is provided by P. A. Gruber, et al.,Low-Cost Wafer Bumping, IBM J. Res. & Dev., Vol. 49 No. 4/5(July/September 2005), hereby incorporated by reference. IMS has foundapplicability to flip-chip wafer bumping and CCGA substrate formation.Broadly, IMS wafer bumping is a two-step process in which solder isinjected into a mold and subsequently transferred to the surface of awafer or substrate using a reflow process. The IMS method allows for thecontrolled injection of molten solder using a variety of moldgeometries. Thus the use of IMS has been extended beyond wafer bumpingto other microelectronic interconnections, e.g., solder ball and soldercolumn arrays as well as ceramic and organic chip carriers. IMStechniques are further adaptable to the use of a variety of Pb-freesolders, including both ternary and quaternary alloys, thus, making theuse of IMS more attractive as the microelectronics field moves from PbSnto Pb-free solder and other solder materials.

Even with the developments related to the microelectronicinterconnections field, described above, however, significant challengeshave yet to be effectively overcome. One of these problems ismicroelectronic interconnection non-coplanarity. While great pains aretaken to create wafers and substrates with planer surfaces variationsstill remain. The result of depositing solder material interconnectorson non-planar wafers and substrates is non-coplanar interconnectors thatnegatively impact the resulting microelectronic interconnections. Inaddition, an efficient means for the creation of coplanarinterconnectors that are comprised of more than a single solder materialtype and/or capable of having various shape geometries has yet to bedeveloped in the field.

A need has therefore been recognized in connection with providing aneffective means for achieving coplanar interconnectors and coplanarmicroelectronic interconnections.

SUMMARY OF THE INVENTION

There is broadly contemplated, in accordance with at least one presentlypreferred embodiment of the present invention, a method and apparatusfor depositing solder material on a wafer, substrate, or other componentof an electrical package in which a compliant mold having a rigid firstside that is planar and a second side that is compliant, and having oneor more conduits or cavities therein. In at least one embodiment of themethod and apparatus of the present invention the use of an IMS head isused to flow the solder material into the conduits or cavities of thecomplaint mold. Broadly, the complaint mold is positioned between theIMS head and the receiving wafer, substrate, or other component of anelectrical package with the complaint side adjacent to wafer, substrate,or other component of an electrical package and the planar side adjacentto the IMS head. Solder material is flowed from the IMS head into thecompliant mold conduits or cavities and onto the wafer or substrate. Inat least one embodiment of the present invention, the complaint moldfurther comprises two materials wherein the first material is rigid andforms the planar side of the complaint mold and the second material isless rigid and forms the complaint side of the complaint mold.Furthermore, a second complaint mold with conduits and/or cavities orreduced compression can be used in conjunction with the first mold aftera first pass filling process has been performed. Thus creatingadditional cavities spaced directly adjacent to the first fill structureis also contemplated as a part of the method and apparatus of at leastone embodiment of the present invention, whereby these cavities and/orconduits can be used to add additional solder material deposits to awafer, substrate, or other component of an electrical package.

A first embodiment of the present invention is an apparatus fordepositing coplanar solder material interconnectors on a wafer, saidapparatus comprising: a first compliant mold having a plurality ofconduits for receiving the solder material; and an injection moldsoldering head for injecting the solder material, wherein said compliantmold is positioned between said injection mold soldering head and saidwafer.

A second embodiment of the present invention is an apparatus fordepositing coplanar solder material interconnectors on a wafer, saidapparatus comprising: a first compliant mold having a plurality ofconduits for receiving the solder material; an injection mold solderinghead for injecting the solder material, wherein said compliant mold ispositioned between said injection mold soldering head and said wafer;and a second compliant mold having a plurality of conduits for receivingsolder material, wherein said second compliant mold is positionedbetween said injection mold soldering head and said wafer wherebyadditional solder material is deposited onto said wafer.

A third embodiment of the present invention is an apparatus fordepositing coplanar solder material interconnectors on a wafer, saidapparatus comprising: a compliant mold having a plurality of conduitsfor receiving the solder material; an injection mold soldering head forinjecting the solder material, wherein said compliant mold is positionedbetween said injection mold soldering head and said wafer and a firstpass solder is deposited while compressing the compliant mold; and asecond or additional mold filling process is completed with an alternatesolder composition while reduced force against the compliant mold isemployed so as to leave additional solder adjacent to the first passsolder deposition and wherein said second pass of solder filling thecompliant mold is positioned between said injection mold soldering headand said wafer whereby additional solder material is deposited onto saidwafer.

In a another embodiment of the present invention a method for depositingcoplanar solder material interconnectors on a wafer, comprising thesteps of: placing a compliant mold having a plurality of conduits forcontaining said solder material between an injection mold soldering headand said wafer receiving said solder material; injecting said solderingmaterial into said conduits; and after said injecting step removing saidcomplaint mold.

In another embodiment of the present invention there is a method fordepositing coplanar solder material interconnectors on a wafer withraised stud interconnections (Cu, metallic or polymer/metal compositestuds, pillars, tubes, probes and/or seal band), comprising the stepsof: placing a compliant mold having a plurality of conduits forcontaining said solder material between an injection mold soldering headand said wafer with raised interconnections receiving said soldermaterial; injecting said soldering material into said conduits; andafter said injecting step removing said complaint mold.

In another embodiment of the present invention there is a method fordepositing coplanar solder material interconnectors on a substrate,comprising the steps of: placing a compliant mold having a plurality ofconduits for containing said solder material between an injection moldsoldering head and said substrate receiving said solder material;injecting said soldering material into said conduits; and after saidinjecting step removing said complaint mold.

For a better understanding of the present invention, together with otherand further features and advantages thereof, reference is made to thefollowing description, taken in conjunction with the accompanyingdrawings, and the scope of the invention will be pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a compliant mold in accordance with atleast one embodiment of the present invention, including holes or cavityformations.

FIG. 2 schematically a compliant mold in accordance with at least oneembodiment of the present invention, including one compliant side andone planer side.

FIG. 3 schematically illustrates a compliant mold aligned over a waferin accordance with at least one embodiment of the present invention.

FIG. 4 schematically illustrates depositing of solder through complaintmold in accordance with at least one embodiment of the presentinvention.

FIG. 5 schematically illustrates a wafer in accordance with at least oneembodiment of the present invention having coplanar solderinterconnectors.

FIG. 6 schematically illustrates a wafer and aligned mold in accordancewith at least one embodiment of the preset invention and the depositingof a first solder material through complaint mold in accordance with atleast one embodiment of the present invention.

FIG. 7 schematically illustrates depositing of a second solder materialthrough complaint mold in accordance with at least one embodiment of thepresent invention.

FIG. 8 schematically illustrates a wafer in accordance with at least oneembodiment of the present invention having coplanar solderinterconnectors consisting of two solder materials per interconnector.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, in FIG. 1 there is shown a compliant mold 10in accordance with one preferred embodiment of the present invention.Complaint mold 10 may be formed from various materials based on thedurometric properties associated with the particular material in lightof the compliance requirements. Examples of the materials forming thecompliant mold include polymer grid material, temperature resistantrubber, silicon based polymers, polyimide based polymers, as well asother alternative compliant materials. Furthermore, as illustrated inFIG. 2, the compliant mold 10 can be formed as a laminated structurehaving multiple layers. It is important that the material be formed suchthat it will have at least one compliant side 20 adaptable tocompression and a more rigid side 30 to ensure proper planarity andcable of the mold-wafer/substrate alignment discussed below oralternatively the non-contact side (away from wafer or substrate) mayprovide a planar surface based on the injection mold head providing aplanar surface while depositing solder into cavities and whilecompressing the compliant mold. In at least one preferred embodiment ofthe present invention the complaint mold is comprised of two layers,namely, a rigid top surface layer 30 with an underlying complaint layer20. The planar rigid side 30 can be made of various materials known inthe art including, inter alia, glass, borosilicate glass, silicon,silicon oxide, polymer based materials, polymer coated metal, metal, andplastic. Choice of material can be determined by many factors such asthe coefficient of thermal expansion, cavity interconnection featuresize and alignment accuracy to the wafer or substrate as well as themechanical properties of the mold. For example, the use of borosilicateglass or silicon as the rigid planar side material of the compliant mold10 can support not only co-planarity for solder deposition but alsocontrolled alignment and CTE management of the compliant portion of themold (i.e., high temperature rubber or silicone rubber) relative to thewafer or substrate receiving solder deposition through this IMS process.Compression of the composite/ compliant mold against the wafer orsubstrate receiving solder and choice of IMS head gasket can preventsolder leakage during processing. Thus a mold could be a silicon waferwith adhered thin silicon rubber on one side with appropriately etchedcavities in silicon and silicone rubber for use against a silicon waferand could be a polymer coating on a thin copper plate with a hightemperature silicone rubber layer on one side that could then contact anorganic package or board with similar CTE. Furthermore, the compliantmold 10 as shown in accordance with a presently preferred embodiment ofthe invention includes formed conduits 40 allowing solder material to beformed in a desired shape, as well as allowing for the controlleddepositing of the material onto the wafer, substrate, or board. Itshould be clearly appreciated that the conduits 40 can take on a varietyof shapes and sizes depending upon the application. Such shapes mightinclude holes, columns, cavity formations, and seal bands. Such conduits40 in the compliant mold 10 can be made using a verity of techniquesdepending upon the type of material used for the formation of the mold.

For example, hole formation in silicon may be made by reactive ionetching and subsequent oxidation to provide a good cavity, goodmechanical wear properties and desired surface properties resistant toreaction with solder. For borosilicate glass, cavities may be formed bychemical etching. For compliant rubber or silicone rubber materials,cavities can be formed by laser ablation or alternate means. Holes orcavities in polymer may be formed by photolithographic processes, laserablation or rather than subtractive processes by additive build up ordeposition processes.

As shown in FIG. 3, the complaint mold 10 is aligned with the wafer orsubstrate 50. The alignment methodology can utilize pins, opticalalignment pads, edge references, prior attachment pins or balls, as wellas other alternative methods known in the art. Conduits or cavities 40in the compliant mold 10 are formed in a pattern mirroring the receivingpads 60 on the wafer or substrate 50. After the proper alignment isachieved, the complaint mold 10 and wafer or substrate 50 combinationcan be held together by clamping, applied pressure, or other methodsknown in the art.

As shown in FIG. 4, in a preferred embodiment of the invention an IMShead 70 scans the compliant mold 10 filling the compliant mold conduits(or cavities) 40 with injected solder material 80. It should beappreciated that a variety of solder materials could be injected intothe mold holes or cavities. Such solder compositions are known in theart and include conductive polymers, high lead solder (e.g., 97Pb, 3Sn;95Pb, 5Sn; 90Pb, 10Sn), eutectic solder (e.g., 37Pb, 63Sn), and leadfree solder (e.g., 97.5Sn, 2.5Ag; SnAgCu (SAC eutectic alloy); SnCu(99.3Sn, 0.7Sn); AuSn (80Au, 20Sn); In; or Sn), as well as otheralternative materials capable of providing electrical interconnections.Referring to FIG. 4, the conduits or cavities 40 are filled toapproximately the level of the top rigid planar side 30 of the compliantmold 10. Where multiple conduits or cavities are filled by the IMS head70 they are filled to the same level relative to the complaint mold'stop rigid planar surface 30, thereby creating a coplanar surface ofinterconnectors 90, as shown in FIG. 5.

A metallurgical bond is established between the solder material 80 andthe wafer or substrate 50 through known means, e.g., in wafer bondingsolder can form attachments to BLM pads deposited on the wafer throughsolder “wetting” methods known to one skilled in the art. One may useflux processes and subsequent cleaning after solder joining to the BLMor copper studs; one may use no clean fluxes or formic acid enrichednitrogen atmosphere as examples of means to achieve good solderattachment to the contact pad on the wafer or substrate. Upon cooling,the solder material is more strongly bonded to the wafer or substratepads 60 than to the compliant mold's conduits or cavities 40. Thus, uponthe removal of the compliant mold 10, as shown in FIG. 5, a wafer orsubstrate 50 is formed having microelectronic interconnectors 90 with acoplanar surface, i.e., terminal end of each interconnector opposite tothe interconnector-wafer or substrate attachment are coplanar with oneanother. The resulting wafer or substrate 50 can be used to formsubsequent microelectronic interconnections. At this point the surfacefeatures can be coplanar based on solder injection molding by means of acoplanar process. Another means to achieve a coplanar surface is the useof a mechanical planar surface coining to flatten the top surface of thesolder connections to create a coplanar surface subsequent to this IMSdeposition process. Another method to achieve coplanarity of theinterconnection surfaces is to use copper studs on the wafer which canbe coined or which can receive solder depositions on their surfaces witheither a one step coplanar deposition or subsequent coining of depositedsolder to form a coplanar surface.

A second preferred embodiment of the present invention is illustrated inFIGS. 6-8. IN a process similar to the method described above, multiplelayers of varying solder material compositions can be deposited, i.e.,stepped or built up, onto the surface of a wafer or substrate;therefore, it should be appreciated that the second embodiment enablesthe creation of microelectronic interconnectors wherein eachinterconnector is made of a plurality of soldering materials, which cantake various forms, e.g., a stepped, side-by-side, encapsulation, etcetera.

As shown in FIG. 6, a first compliant mold 100 is aligned with a waferor substrate 110 and a first high-melt solder material 120 is depositedonto the wafer or substrate 110 by the IMS head 70 at high compressionvia the compliant mold conduits or cavities 130. After the first soldermaterial 120 is cooled and bonded to the wafer or substrate 110 and thefirst compliant mold 100 is removed a second compliant mold 200 havingreduced compression durometric properties is aligned with the wafer orsubstrate 110 as illustrated in FIG. 7. A second IMS head scan isperformed wherein a second solder material 220 having lower meltingpoint characteristics is deposited in combination with the first soldermaterial 120. The second complaint mold 200 is subsequently removedyielding a wafer or substrate 110 having coplanar interconnections 290each of which is comprises two different solder materials as shown inFIG. 8. It should be appreciated that a number of different compliantmolds could be used in a similar manner to create coplanarinterconnectors made of a plurality of solder materials. Furthermore, itcan also be appreciated by one skilled in the art that multiplecompliant molds may be used to form layered or stepped multi-materialsolder interconnections as well as encapsulated compositions, i.e., afirst deposited solder material could be enclosed by a second depositedmaterial. Furthermore, it can be appreciated by one skilled in the artthat a single compliant mold could be used to deposit a first passsolder deposition with higher compression of the mold followed by asecond pass or passes at reduced pressure and reduced compression of thecompliant mold, which can provide more than one solder deposition usingthe same mold and cavity per interconnection.

Likewise it should also be appreciated that multiple shapes ofinterconnectors could be formed using the method and apparatus of thepresent invention. For example, in another embodiment of the presentinvention a first complaint mold is used to deposit solder materialhaving a first shape in the fashion described above onto a wafer orsubstrate. A second complaint mold is then used to deposit anothersolder material having a second shape. Thus geometries which might nototherwise be capable of formation in a single mold process can be formedin an efficient manner. For example, a first compliant mold could beused to deposit a particular interconnector shape, while a secondcompliant mold could be used to subsequently create seal bands. Itshould be appreciated the method of the present embodiment could be usedto make solder deposit interconnectors with unique shapes havingcombinations of traditional metal based solder materials and polymersolder materials.

Although illustrative embodiments of the present invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments, and that various other changes and modifications may beaffected therein by one skilled in the art without departing from thescope or spirit of the invention.

1. A method for depositing coplanar solder material interconnectors on awafer, comprising the steps of: placing a first compliant mold having aplurality of conduits for containing said solder material between aninjection mold soldering head and the wafer receiving said soldermaterial; injecting said soldering material into said conduits; andafter said step of injecting the solder material, removing said firstcomplaint mold; wherein said first complaint mold comprises: a firstplanar side; and a second compliant side; and wherein said first planarside and said second complaint side are separate layers of material. 2.The method according to claim 1, wherein: said compliant side is amaterial selected from the group consisting of rubber, silicon, andcompliant polymer based material.
 3. The method according to claim 1,wherein: said planar side is a material selected from the groupconsisting of silicon, silicon oxide, glass, and polymer coated metal.4. The method according to claim 1, wherein: said first complaint moldis formed of a single material.
 5. The method according to claim 1,further comprising the steps of: placing a second compliant mold havinga plurality of conduits for receiving solder material between theinjection mold soldering head and the wafer whereby additional soldermaterial is deposited onto said wafer.
 6. A method for depositingcoplanar solder material interconnectors on a substrate, comprising thesteps of: placing a first compliant mold having a plurality of conduitsfor containing said solder material between an injection mold solderinghead and the substrate receiving said solder material; injecting saidsoldering material into said conduits; and after said step of injectingthe solder material, removing said first complaint mold; wherein saidfirst complaint mold comprises: a first planar side; and a secondcompliant side; and wherein said first planar side and said secondcomplaint side are separate layers of material.
 7. The method accordingto claim 6, wherein: said planar side is a material selected from thegroup consisting of silicon, silicon oxide, glass, and polymer coatedmetal.
 8. The method according to claim 6, further comprising the stepsof: placing a second compliant mold having a plurality of conduits forreceiving solder material between the injection mold soldering head andthe substrate whereby additional solder material is deposited onto saidsubstrate.
 9. The method according to claim 1, wherein said soldermaterial comprises one or more of high lead solder, eutectic solder, andlead free solder.
 10. The method according to claim 6, wherein saidsolder material comprises one or more of high lead solder, eutecticsolder, and lead free solder.
 11. A method comprising: placing acompliant mold having a plurality of conduits for containing soldermaterial between an injection mold soldering head and a substratereceiving said solder material; injecting said soldering material intosaid conduits such that said solder material interconnectors aredeposited on said substrate; and removing said complaint mold; whereinsaid complaint mold comprises: a first planar side; and a secondcompliant side, said second compliant side being a material selectedfrom the group consisting of rubber, silicon, and compliant polymerbased material; and wherein said first planar side and said secondcomplaint side are separate layers of material.
 12. The method accordingto claim 11, wherein: said first planar side is a material selected fromthe group consisting of silicon, silicon oxide, glass, and polymercoated metal.
 13. The method according to claim 11, further comprising:positioning a second compliant mold having a plurality of conduits forreceiving solder material between said injection mold soldering head andsaid substrate whereby additional solder material is deposited onto saidsubstrate.
 14. The method according to claim 11, wherein said soldermaterial comprises one or more of high lead solder, eutectic solder, andlead free solder.